The invention is in the field of screw threads adapted to couple tubes, pipes and rods together. The screw threads are related to dry seal taper pipe threads for connecting adjacent ends of pipes together; without a threaded coupling.
A prior art pipe connection is illustrated in FIG. 1. Pipes 10 and 11 are standard metal or plastic tubular members having standard taper pipe threads 13 and 14. The standard pipe thread taper is 1 inch for every 16 inches in the length of the pipe. The number of threads per inch of pipe changes with the pitch diameter of the thread. The number of acme threads per inch is from 2 for large diameter pipes to 16 for small diameter pipes. The last thread 15 is a partial thread due to chamber on the die used to cut the thread. A tubular coupling 12 having internal threads 16 and 17 holds pipes 10 and 11 in end to end relationship. Threads 13, 16 and 14, 17 operatively engage each other to provide a structural connection between coupling 12 and pipes 10 and 11. The interengaging threads 13, 16 and 14, 17 also seal coupling 12 on pipes 10 and 11 to prevent fluids from entering the pipe passage and leakage of fluids from the pipes. The longitudinal axes of pipes 10 and 11 must be axially aligned with the longitudinal axis of coupling 12 to turn coupling 12 onto pipe 10 or turn the pipes into coupling 12. Pipe 11 must be axially aligned with coupling 12 and retained in axial alignment to prevent cross threading as pipe 11 is turned about it""s longitudinal axis to thread pipe 11 into coupling 12. Axial alignment of large long pipes having standard pipe threads and turning of the pipes to prevent cross threading is a difficult procedure which requires considerable time and labor. The coupling 12 is a tubular sleeve that fits around the outside of adjacent ends of the pipe which prevents pipe connects with a coupling from being closely fitted into round and square passages of tubes and tubular beams.
The invention is a connecting structure for pipes, tubular members and cylindrical rods, such as metal and plastic pipes, and metal and plastic rods. The connecting structure is incorporated in female and male ends of pipes. Separate external or internal coupling or threaded sleeves are not used to join pipes in end-to-end relation. The sizes of the pipes passages are not altered so that the flow of fluid in the passages is not impeded. The exposed outside walls of the pipes have uniform dimensions and sizes which allow connected pipes to be placed with a close or contact fit inside tubes and box beams. The female end of a first pipe has a continuous internal thread. A continuous external thread is on the male end of a second pipe. The internal and external threads are complementary to each other so that when the threads are fully engaged the first and second pipes are rigidly connected in end-to-end relation. The threads have a novel profile and taper that allows for misaligned of the pipes during the pipe connecting process without cross threading of the threads. Each of the threads have an inwardly inclined leading wall extended between a generally flat outer wall and a generally flat inner wall. A radial trailing wall opposite the leading wall extends from the rear of the outer wall to the inner wall. The outer and inner walls of the threads taper axially inward relative to the longitudinal axes of the pipes. This allows the pipes to be turned relative to each other with a minimum of torque. When the pipes are in full or complete engagement, the threads lock up to rigidly connect the pipes together.
The preferred embodiment of the pipe connecting structure attaches generally aligned pipes together in a sealed relationship without external or internal couplings. The pipes have novel cooperating internal and external threads on female and male ends that allow for misaligned without cross threading of the threads. The female end of the first pipe has an annular flange provided with a tapered first internal annular surface. A tapered second internal annular surface is spaced axially inward from the first internal annular surface. An internal thread extends between the first and second internal surfaces. The male end of a second pipe is of a size that turns into the female end of the first to connect the pipes together. The male end has a annular sleeve having a first tapered outer annular surface with a size adopted to be located in tight surface engagement with the second internal surface. A tapered second external annular surface spaced axially inward from the first outer annular surface has a size to fit with tight surface engagement with the first internal surface. A continuous external thread extends between the first and second outer cylindrical surfaces. The external and internal threads are complementary to each other so that when the threads are fully engaged the threads lock up and the adjacent internal and external annular surfaces are in tight surface engagement with each other. Each of the threads have an inwardly inclined leading wall with an angle of about 45 degrees relative to the longitudinal axis of the pipe associated with the thread. The leading wall extends between a generally flat outer wall and a generally flat inner wall. A radial trailing wall opposite the leading wall extends radially from the rear of the rear wall to the inner wall. The outer and inner walls each have a length that is about twice the height of the trailing wall. The outer and inner walls have the same axially inward taper which is the same taper as the annular surfaces. The pitch diameters of the threads also have the same taper as the outer and inner walls of the threads. This taper is, for example, one degree relative to the longitudinal axes of the pipes.